1. Field of the Invention
This invention relates to an improvement on a centrifugal pump. This centrifugal pump is suitable for use as an automobile centrifugal water pump for circulating engine cooling water.
2. Description of the Prior Art
Automobile centrifugal water pumps are classified into two types. One type is driven independently by a motor, a hydraulic actuator and the like without utilizing the rotation of an engine. The other type is connected to an engine by way of a belt and driven by utilizing the rotation of an engine together with a generator and an air-cooling fan.
When a centrifugal water pump driven by a motor is employed, the capacity of a battery and a generator should be increased, because the electricity consumption increases. When a centrifugal water pump driven by a hydraulic actuator is employed, extra apparatuses are required for the cooling system. Whereby the system gets complicated as a whole, the cost thereof gets expensive, and the space occupied by the system and the weight thereof increases.
On the other hand, when a centrifugal water pump driven by utilizing the rotation of an engine is employed, the system has the following advantages, i.e., the system is simple, the system fails less, and the system is efficient. However, the system has the following disadvantages as well, because the number of the revolutions of the centrifugal water pump increases or decreases in proportion to the number of the revolutions of the engine.
Namely, the flow amount of the cooling water is likely to become insufficient when the engine is running at low speeds, and the flow amount thereof is likely to get unnecessarily large when the engine is running at high speeds, because the number of revolutions of the engine falls in a very wide range. This results from the fact that the configuration of the turbine of the centrifugal water pump remains the same, and the dimensionless characteristic thereof accordingly always remains the same.
Consequently, a centrifugal water pump is proposed whose capacity is made variable by varying the configuration of the turbine. However, the pump capacities of the conventional centrifugal water pumps of this type are varied by utilizing the expansion and contraction of thermo-wax, or by utilizing the shape memory effect of shape memory alloy, thereby varying the configuration of the blades (for instance, varying the height of the blades), or thereby varying the installation angle of the blades. The pump capacities of these conventional centrifugal water pumps are made variable in accordance with the temperatures of the cooling water, and these conventional centrifugal pumps do not have a mechanism enabling the making of the pump capacities variable in accordance with the number of revolutions of the engine.